1. Technical Field
The present invention relates to a method for manufacturing a piezoelectric element, and to a piezoelectric element, a liquid ejecting head and a liquid ejecting apparatus.
2. Related Art
Ink jet recording heads are a typical type of liquid ejecting head. An ink jet recording head includes a vibration plate defining a part of a pressure generating chamber communicating with nozzle apertures through which ink droplets are ejected. In the ink jet recording head, a piezoelectric element deforms the vibration plate to apply a pressure to the ink in the pressure generating chamber, thereby ejecting ink droplets through the nozzle apertures. Some of the piezoelectric elements used in ink jet recording heads have a structure in which a piezoelectric layer made of a piezoelectric material capable of electromechanical conversion, such as a piezoelectric ceramic, is disposed between two electrodes. This type of piezoelectric element is used as a deflection vibration mode actuator device in a liquid ejecting head.
A liquid ejecting head has been known which uses lead zirconate titanate (PZT) having a high displacement property as a piezoelectric ceramic. However, lead zirconate titanate contains lead. From the viewpoint of environmental protection, lead-free piezoelectric materials are desired.
Accordingly, piezoelectric materials have been developed which do not contain lead, but have piezoelectric properties equal to PZT. For example, piezoelectric materials having a bismuth ferrate-based (BiFeO3-based) perovskite structure containing bismuth and iron have been proposed. JP-A-2009-252789 discloses an example of such materials which is a complex oxide expressed as a mixed crystal of bismuth ferrate manganate such as Bi(Fe,Mn)O3 and barium titanate such as BaTiO3. Piezoelectric materials containing an alkali metal have also been developed, such as bismuth sodium titanate (BiNaTiO3, hereafter simply referred to as BNT).
Lead-free bismuth-containing piezoelectric materials are promising as an alternative to PZT. However, if a piezoelectric element is formed using such a bismuth-containing piezoelectric material, bismuth in the material is likely to diffuse into the electrodes, thereby causing film separation.
More specifically, if a bismuth-based piezoelectric layer is formed after a first electrode of platinum or the like has been formed on an insulating layer of, for example, zirconium oxide with a titanium oxide adhesion layer therebetween, as with PZT piezoelectric elements, the bismuth in the piezoelectric layer diffuses into the first electrode and, further, precipitates out at the interface between the first electrode and the underlying adhesion layer. This precipitate causes undesired film separation. If the adhesion layer contains titanium, the titanium diffuses into the first electrode and further into the piezoelectric layer simultaneously with the diffusion of bismuth into the first electrode. Consequently, the properties of the piezoelectric layer are undesirably degraded.
In any case, it is difficult to produce a high-performance piezoelectric element including a piezoelectric layer that is made of a lead-free bismuth-based piezoelectric material and maintains an adhesion with the underlying layer.
Other types of liquid ejecting heads have the described disadvantages. Not only ink jet heads, but also piezoelectric elements used in other devices, such as ultrasonic devices, in addition to elements used in liquid ejecting heads, have the described disadvantages.